1. Field of the Invention
The present invention relates to an image processing apparatus which controls a fixing temperature of a fixing device in fixing, on a recording sheet, a toner image formed employing an electrophotographic method, and relates to an image processing method thereof and a storage medium.
2. Description of the Related Art
An image forming apparatus which heat-fixes, on the recording sheet, the toner image formed employing the electrophotographic method, determines the fixing temperature of the fixing device according to an amount of color material per unit area to be applied to the recording sheet. Normally, a maximum value of the amount of color material per unit area is predetermined. The image forming apparatus thus adjusts the fixing temperature so that an image formed using such maximum amount of color material can be steadily fixed on the recording sheet.
A full-color copying machine superimposes a plurality of color materials, i.e., cyan (C), magenta (M), yellow (Y), and black (B) color materials, to form the image. The amount of color material (hereinafter referred to as a toner amount) applied to the recording sheet thus tends to increase, and heat capacity of a fixing roller becomes large. If the temperature of the fixing device is lower than the preset temperature, such as when the full-color copying machine is switched on, or is recovering from a sleep state, a fixing warm-up time for the temperature to rise to the preset temperature becomes long. As a result, a print-start waiting time is required in the full-color copying machine. Further, the full-color copying machine may output an image whose toner amount is much smaller than the assumed maximum value. For example, when the full-color copying machine outputs an image in a monochromatic printing mode which only uses the black (K) color material, the full-color copying machine applies excessive heat, so that power is wasted.
To reduce the above-described power consumption, Japanese Patent Application Laid-Open No. 2009-151102 discusses a setting that, when a power saving mode is designated, the fixing temperature of the fixing device is set according to a power-saving setting value. A toner application amount value which can be fixed at the set fixing temperature is then calculated, and image processing is performed according to the calculated toner application amount value.
However, the technique discussed in Japanese Patent Application Laid-Open No. 2009-151102 reduces the toner application amount in all pages included in a print job. If the print job includes a number of pages having portions of high toner density, image quality deterioration increases.